At present, as it is shown in the patents of utility model ZL93217054.4 and ZL97239243.2, the oil storage tank with inner floating roof adopts I-shaped or circular components, which are usually processed from steel plate or aluminum plate. These components are constructed into derivative frame network structure by bolts or aluminum rivets, in which a foamed plastic float covered by metallic layer, or a seamless floating tube extruded by aluminum alloy is fixed. A steel plate or aluminum plate is covered at the top of the derivative frame as a cover board, whose edge is sealed with ligulae or wave sealing strip. The inner floating roof is connected with the top of the oil storage tank by a metal lead in order to induce to static electricity. The disadvantage of the present technology are as follow: the complicated structure will result in too much workload when it is locally assembled; its heavy weight with unequally distributed buoyancy which is only 2 to 3 times of its weight will probably result in tumble accident; the whole metal structure of the inner floating roof setting will probably result in the electrostatic damage; the great thickness of the inner floating roof is usually between 100 mm and 400 mm, enlarges the ineffective pace in the oil storage tank's capacity.